The present invention relates to an RF power control circuit of a radio communication device and, more particularly, to an RF power control circuit capable of controlling its transmission power in an unvoice interval of a transmission voice input.
Recently, as radio devices have been made compact and handy, devices driven by a battery have been increasingly manufactured. One of important factors of a portable radio device is a service life of a battery. The service life largely depends on power consumption during transmission.
In order to reduce power consumption to effectively use a battery, some control circuits control such that transmission is performed in only a voice interval of a transmission voice and transmission power is reduced or stopped in an unvoice interval, thereby suppressing power consumption.
In a mobile telephone system used in the North America or England, a control circuit is used to control such that a mobile device always maintains proper transmission power by a command sent from a base station.
FIG. 1 shows a typical conventional control circuit of the latter. In FIG. 1, in accordance with an n-bit selection signal SEI, supplied from a computer 3, a switching circuit 1 selects one of 2.sup.n DC voltages obtained by dividing a DC voltage applied to a terminal 5 by resistors 9 and outputs a reference voltage REF for power control from an output terminal 6.
In order to easily realize the above two types of control circuits, a control signal CS1 representing the presence/absence of a transmission voice and a transmission power control signal CS2 received by a radio receiver 7 from a base station are processed by software of a computer 3 to be converted into the selection signal SEL. The switching circuit 1 is controlled by the selection signal SEL to obtain the reference voltage REF at the output terminal 6.
The above conventional RF power control circuits, however, have the following problems.
That is, the control signal CS1 depends on only the presence/absence of a transmission voice and is completely independent of the transmission power control signal CS2 from the base station. For this reason, since the two independent signals CS1 and CS2 must be processed, a processing amount of the software of the computer 3 is increased.
In addition, the computer 3 shown in FIG. 1 performs user interface processing, i.e. checks whether a volume key, a mute key or a conversation end key is depressed and performs certain processing if any key is depressed. Then, the computer 3 performs connection sequence processing for transmitting/receiving signals with respect to the base station, checks whether a command for starting a test mode is input, and if the command is input, performs a test sequence for starting the test mode. Thereafter, the computer 3 returns to the user interface processing. This cycle is repeatedly performed, and each cycle requires several 10 msec. In addition, these processing programs have priority over other programs and no interruption can be made. Therefore, the control signal CS1 from a voice/unvoice identifier 4 can be processed only after the programs are ended (or before the programs are started). For this reason, in the worst case, the n-bit selection signal SEL cannot be output before several 10 msec pass. A man, however, can recognize a voice interruption of 1 msec. That is, if the selection signal SEL is delayed by several 10 msec, a head of a voice is cut.